1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, which is applied to a variety of relatively sliding portions in machine tools and testing equipment and in which a slider is mounted slidable on a track rail with rolling elements interposed therebetween.
2. Description of the Prior Art
In conventional linear motion rolling guide units, the sealing between a track rail and a slider that slides on it is realized by end seals attached to the ends of the slider and under seals attached to the underside of the slider.
A linear motion rolling guide unit as shown in FIG. 6 has been known. FIG. 6 shows a perspective view of one example of a conventional linear motion rolling guide unit. As shown in the figure, the linear motion rolling guide unit includes as main components a track rail 1 having raceway grooves 17 extending longitudinally on both side wall surfaces 18 thereof, and a slider 20 slidably mounted astride on the track rail 1. The slider 20 has a casing 2, which is slidable relative to the track rail 1 and has raceway grooves 16 formed at positions facing the raceway grooves 17 on the track rail 1, a number of rolling elements 4 trapped between the opposing raceway grooves 16 and 17, and end caps 25 attached to the longitudinal ends of the casing 2, the longitudinal direction being the sliding direction of the casing 2.
The end cap 25 has an end seal 19 attached to the end surface thereof that provides the sealing between the track rail 1 and the slider 20. The casing 2 is provided with under seals 3 for sealing the undersides of the casing 2 and end caps 25 and the longitudinal side wall surfaces 18 of the track rail 1. The slider 20 is mounted astride on the track rail 1 and freely slidable relative to it through a number of rolling elements 4 circulating along the raceway grooves 17 in the track rail 1. The rolling elements 4 circulate through raceways formed between the opposing raceway grooves 16 and 17, through direction changing passages formed in the end caps 25 and through return passages 24 formed in the casing 2.
Mounting and dismounting the under seal 3 to and from the casing 2 is not easy because it uses fastening means such as screws. The under seal 3, though it has an advantage of being simple in construction and easily manufactured, also has drawbacks that because the under seal 3 is thin, it is easily deformed by external forces and by positional errors between it and the casing 2 and track rail 1, the casing and track rail having the raceway grooves 16, 17 respectively. Hence, the under seal 3, which is subjected to temperature variations and exposed to lubricants as the slider 20 slides on the track rail 1, might swell and be deformed deteriorating the sealing performance.
There has been known a dust prevention device for linear guide equipment such as disclosed in the Japanese Utility Model No. 98321/1991. In this dust prevention structure for the linear motion bearing apparatus, the axial ends of an under seal are bent inwardly to shape it like a letter U; the inner surfaces of the bent portions of the under seal are provided with engagement projections protruding inwardly; and the outer end surfaces of the end caps are formed with recesses to receive the engagement projections of the under seal.
In an under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 118317/1991, axial ends of the under seal are formed with axially extending projections and end seals are formed at their bottom end surfaces with engagement holes for receiving the projections of the under seal, whereby the under seal is fitted into the end seals having a greater strength to make mounting and dismounting easy and secure a sufficient strength.
In another under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 121220/1991, the axial ends of the under seal are provided with two-pronged projections protruding toward the underside of the slider, the two prongs diverging in a V-shape and being elastically deformable toward each other. The slider has the axial end portions of the underside thereof formed With vertical holes, into which the two-pronged projections of the under seal are fitted, and also with through-holes that intersect the vertical holes perpendicularly and pass through the arm or wing portions of the slider. One of the two prongs fitted into the vertical hole is elastically deformed therein, urging the under seal toward the side surface of the guide rail to bring the side edge of the under seal into sliding contact with the guide rail.
In these under seal apparatuses for the linear motion guide bearings, the under seal is mounted by engaging the projections or prongs formed on the under seal into the engagement holes formed in the slider or end seals.
The conventional linear motion rolling guide units, however, uses different materials for the dust prevention member and the slider, so that they have different thermal expansions as temperature changes. When the thermal expansion of the dust prevention member becomes larger than that of the slider, the dust prevention member will be deflected creating a gap between it and the guide rail or the underside of the casing, with the result that the sealing performance deteriorates, unable to prevent ingress of dust.
The applicant of this invention developed a linear motion rolling guide unit that solved the above-mentioned problem, and applied for patent previously (Japanese Patent Laid-Open No. 164128/1993). In this linear motion rolling guide unit, the under seal has a lip portion sealingly engageable with the undersides of the casing and the end caps and another lip portion sealingly engageable with the side wall surface of the track rail. The under seal is also formed at the longitudinal ends with locking portions, which are fitted into engagement holes formed in the end seals to mount the under seal to the end seals.
In the conventional linear motion rolling guide unit, since the longitudinal ends of the under seal are engaged in the engagement holes formed in the end caps or end seals to mount the under seal to the end seals, there must be some play for the under seal to move relative to the undersides of the casing and end caps so that the longitudinal elongation of the under seal due to thermal expansion difference can be offset by the engagement holes in the end caps or end seals. Otherwise, the under seal would be deformed as by buckling, degrading the sealing performance.
The conventional linear motion rolling guide unit, however, has the construction in which the projections of the under seal are engaged in the engagement holes in the end caps or end seals in such a way that they cannot move in the longitudinal direction. Further, since the under seal adheres to the undersides of the casing and end caps, the under seal cannot move. This structure, though it may facilitate the mounting and dismounting of the under seal, may not necessarily be able to position the under seal correctly and also has a problem that the under seal will be deformed by temperature variations and by swelling due to exposure to lubricants, deteriorating the sealing performance.